1. Field of the Invention
The present invention relates generally to a sheet processing device and an image forming system and, more particularly, to sheet binding.
2. Description of the Related Art
Increasing digitization of information in recent years has made image processing apparatuses such as printers and facsimiles for use in outputting digitized information and scanners for use in digitalizing documents indispensable. Such an image processing apparatus is typically configured as a multifunction peripheral (MFP) having an image capture function, an image forming function, a communication function, and the like and usable as a printer, a facsimile, a scanner, and a copier.
It is known that some type of MFPs is equipped with a binding device that binds a bundle of a plurality of sheets, on which images are formed by the MFP, together. Schemes used by such a binding device in binding a sheet bundle include a scheme (hereinafter, “staple binding”) with use of a metal staple(s) and a scheme (hereinafter, “stapleless binding”) without use of a metal staple.
As such a binding device as that described above, a binding device capable of both staple binding and stapleless binding has been proposed and known. An example is disclosed in Japanese Laid-open Patent Application No. 2004-168435. Binding devices capable of both the schemes are typically configured to perform binding as follows. First, a selected one of a staple binding unit that performs staple binding and a stapleless binding unit that performs stapleless binding is moved from its home position to a binding position. The binding device then receives a sheet bundle into a binding channel of the moved binding unit and sandwiches the received sheet bundle from above and below sheet surfaces, thereby binding the sheet bundle.
Some type of the binding devices capable of both the schemes is configured such that the maximum number of sheets (hereinafter, “maximum sheet count”) that can be bound at a time by staple binding differs from that of stapleless binding. In some binding devices of this type, a compiling unit where sheets are to be stacked in a pile until all to-be-bound sheets are placed therein is designed to have a height adjusted to a larger one of the maximum sheet counts. A binding device configured in this manner can stack, even if the maximum sheet counts differ between staple binding and stapleless binding, a corresponding maximum sheet count of sheets for each of the schemes.
However, when the compiling unit of the binding device is designed to have a height adjusted to a larger one of the maximum sheet counts, the following disadvantage can occur. When a sheet bundle is to be bound using one, which is smaller in the maximum sheet count, of the schemes, even if the sheet bundle contains the maximum sheet count of sheets, a clearance in the direction of sheet thickness is left in the compiling unit. The clearance can cause curling, deflection, or the like to occur in the sheet bundle at a binding position. Accordingly, the binding device configured as described above can have the following problem. When a sheet bundle is to be bound using the one, which is smaller in the maximum sheet count, of the schemes, even if the sheet bundle contains the maximum sheet count of stacked sheets or less, the curling or deflection described above can increase the thickness of the sheet bundle relative to the thickness of the sheet bundle free from the curling, deflection, or the like (hereinafter, “should be thickness”) to exceed opening height of the binding channel. As a result, the sheet bundle cannot be received into the binding channel.
A method of pressing the sheet bundle stacked in the compiling unit of the binding device in the direction of sheet thickness may be applicable. Examples of this method are disclosed in Japanese Laid-open Patent Publication No. 2005-263404 and Japanese Laid-open Patent Publication No. 10-279163. When the binding device is configured to apply this method, occurrence of the curling, deflection, or the like can be reduced even if a clearance in the sheet thickness direction is left in the compiling unit.
However, such a binding device has a disadvantage that arises from the need of pressing a sheet bundle stacked in the compiling unit in the sheet thickness direction. That is, a pressing member that presses the sheet bundle can interfere with sheet conveyance. This disadvantage can be avoided by configuring the binding device to include compiling units independently, one for staple binding and the other for stapleless binding. However, this configuration disadvantageously increases manufacturing cost and device size due to an increase in the number of parts and control systems.
Therefore, there is a need for a sheet processing device capable of binding sheets without interfering with sheet conveyance with an inexpensive, compact, and simple configuration.